Chromate removal by precipitation
AssigneeHuron Chemicals Limited
InventorsBruno Kindl, Jennifer Geraldine Atkinson
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Abstract
Chromates are removed from aqueous alkali metal chlorate solutions by either of two processes. In the first process, a water-soluble sulfide is added to react with the chromate, and then a ferrous salt is added. The soluble sulfate is converted to elemental sulfur and the chromate is converted to an insoluble trivalent Cr-containing material which is removed from solution. In the second process an "iron mud" is prepared by reacting a ferrous salt with sodium hydroxide and added so as to precipitate insoluble trivalent chromium-containing material.
Claims16
A method of removing chromate from aqueous alkali metal chlorate solutions which comprises:
- adding to a chromate-containing aqueous solution of an alkali metal chlorate, at a temperature of about 40.degree. to about 60.degree. C, a water-soluble sulfide in an amount ranging from about 70 to about 200% of the stoichiometric value required to react with said chromate, said aqueous solution having an initial pH in the range of 7-8;
- then adding to said solution a water-soluble ferrous salt in an amount ranging from about 30 to about 100% of the stoichiometric value required to react with said chromate, and adjusting the pH of the solution such that the final pH is in the range of about 1.8 to about 3.0, whereby said chromate is converted to an insoluble trivalent chromium-containing material and the sulfide is completely converted to elemental sulfur;
- and
- separating said insoluble trivalent chromium-containing material from said solution.
A method of removing chromate from aqueous alkali metal chlorate solutions which comprises:
- adjusting the pH of a chromate-containing aqueous solution of an alkali metal chlorate to a value within the range of from about 7 to about 11, said solution having a temperature of about 40.degree. to about 60.degree. C;
- adding to said solution the product obtained by reacting a ferrous salt with an alkali metal hydroxide in relative proportions of 1 part ferrous salt to 1.5-1.8 parts of said alkali metal hydroxide, the amount of said ferrous salt employed being from about 3 to about 5 times the stoichiometric amount required to reduce the chromate present in the solution, said addition being effected slowly, and simultaneously with strong agitation, and said pH being controlled to a value within the range of 10-12, whereby said chromate is converted to an insoluble trivalent chromium-containing material;
- and
- separating said insoluble trivalent chromium-containing material from said solution.
A method according to claim 13 wherein there is added to the solution an Fe mud obtained by reacting FeSO.sub.4 . 7H.sub.2 O with NaOH in a molar proportion of 1.7 moles NaOH per 1 mole FeSO.sub.4.
Dependencies are inferred from the claim text.